Valve systems are commonly used in various operations or processes for controlling the flow of fluid to and from a cylinder or other such actuating device having a movable work performing member or armature. However, the device is not constantly in motion, with the work performing member being held in a stationary position during various portions of the operation. Maintaining full line control pressure during periods when the movable work performing member is in the stationary position has been found to be wasteful of energy required to run compressors or other such sources of fluid power.
Fluid leakage inevitably occurs in the fluid power operated device or in related systems or subsystems. Maintaining full line control pressure and flow in order to compensate for such leakage has also been found to be expensive and wasteful in terms of energy usage, especially in systems such as those described above where a movable work performing member is required to be held in a stationary position during various portions of the operation of the system.
One particular system employing such devices is a system for processing molten metal. Typical processing systems include a large receptacle for retaining a mass of molten metal. The surface of the molten metal is generally exposed to atmosphere and thus exothermic heat transfer occurs from the mass, thereby cooling the top surface of the mass and forming a crust. The crust formation is detrimental to the material processing, thus fluid power operated devices are commonly employed for intermittently breaking the crust. As a result, energy is unnecessarily expended by maintaining the fluid power operated devices in a stationary position.
In the event that fluid pressure is lost within the fluid power operated devices, these devices may come into extended contact with the molten metal. This contact with the molten metal results in heat transfer from the mass to the devices and can cause the devices to become embedded in the molten metal. This type of contact has been found to reduce energy efficiency because additional heat is required to compensate for heat lost through the heat transfer.